linux-kernel - Re: [PATCH 2/3] rust: maple_tree: add MapleTree::lock() and load()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAH5fLgjB7-xJ2OjVa6nxnUPk-1+wyxPMWQ15-Vc3mUp36+_Rhg@mail.gmail.com>
Date: Sat, 26 Jul 2025 18:18:02 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Gary Guo <gary@...yguo.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Andrew Ballance <andrewjballance@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, linux-kernel@...r.kernel.org, 
	maple-tree@...ts.infradead.org, rust-for-linux@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH 2/3] rust: maple_tree: add MapleTree::lock() and load()

On Sat, Jul 26, 2025 at 6:15 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> On Sat, Jul 26, 2025 at 5:50 PM Gary Guo <gary@...yguo.net> wrote:
> >
> > On Sat, 26 Jul 2025 13:23:23 +0000
> > Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > > To load a value, one must be careful to hold the lock while accessing
> > > it. To enable this, we add a lock() method so that you can perform
> > > operations on the value before the spinlock is released.
> > >
> > > Co-developed-by: Andrew Ballance <andrewjballance@...il.com>
> > > Signed-off-by: Andrew Ballance <andrewjballance@...il.com>
> > > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> > > ---
> > >  rust/kernel/maple_tree.rs | 94 +++++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 94 insertions(+)
> > >
> > > diff --git a/rust/kernel/maple_tree.rs b/rust/kernel/maple_tree.rs
> > > index 0f26c173eedc7c79bb8e2b56fe85e8a266b3ae0c..c7ef504a9c78065b3d5752b4f5337fb6277182d1 100644
> > > --- a/rust/kernel/maple_tree.rs
> > > +++ b/rust/kernel/maple_tree.rs
> > > @@ -206,6 +206,23 @@ pub fn erase(&self, index: usize) -> Option<T> {
> > >          unsafe { T::try_from_foreign(ret) }
> > >      }
> > >
> > > +    /// Lock the internal spinlock.
> > > +    #[inline]
> > > +    pub fn lock(&self) -> MapleLock<'_, T> {
> > > +        // SAFETY: It's safe to lock the spinlock in a maple tree.
> > > +        unsafe { bindings::spin_lock(self.ma_lock()) };
> > > +
> > > +        // INVARIANT: We just took the spinlock.
> > > +        MapleLock(self)
> > > +    }
> > > +
> > > +    #[inline]
> > > +    fn ma_lock(&self) -> *mut bindings::spinlock_t {
> > > +        // SAFETY: This pointer offset operation stays in-bounds.
> > > +        let lock = unsafe { &raw mut (*self.tree.get()).__bindgen_anon_1.ma_lock };
> > > +        lock.cast()
> > > +    }
> >
> > Could this return `&SpinLock<()>` using `Lock::from_raw`?
> >
> > I guess it has the drawback of having `MapleLock` needing to store
> > `ma_lock` pointer but the guard is usually just all on stack and
> > inlined so it probably won't make a difference?
> >
> > This way you remove `unsafe` from `lock` and gets a free `drop`.
>
> I ended up going this way to avoid the extra field in MapleLock, like
> you mention.

Oh, and it also avoids assuming anything about the layout of SpinLock<()>

Alice